This invention relates to an electronically controlled seat belt module. More particularly, this invention relates to an electronically controlled seat belt module for a restraint system in a vehicle.
As is known, vehicles, particularly passenger vehicles, are provided with various types of restraint devices in order to reduce the risk of injury to an occupant in the event that the vehicle crashes into another object. These devices include seat belts, such as three point belts, two point belts and the like, to restrain an occupant in a seat during a crash and air bags to cushion an occupant against the effects of a crash.
Typically, a seat belt assembly is constructed with a spool on which a webbing is wound and from which the webbing may be unwound in order to be placed across the lap and/or chest of a seated occupant. In addition, a retractor is provided in order to rewind the webbing onto the spool when the seat belt is not in use. The seat belt assembly is also constructed to lock in place when a crash is sensed in order to anchor the occupant to the seat. That is to say, the seat belt becomes locked so as to restrain a forward movement of the occupant.
In some cases, pretensioners and load limiters have been employed with the seat belt assembly to reduce unnecessary seat belt slack and to maintain the belt force in the webbing at a controlled and pre-defined level. The limiting of the seat belt tension has been accomplished by a mechanism in the retractor of the seat belt assembly that allows the webbing of the seat belt assembly to be pulled out slightly and in a controlled way if the load on an occupant""s body becomes too high in a violent crash. This mechanism has been used in combination with an air bag.
In one known load limiter, a bar is used to hold a spindle on which the spool of webbing is mounted in place. When the force on the webbing exceeds a pre-set limit, usually 4 kN, the end of the bar will turn thereby twisting the bar and spool allowing the webbing to be played out thereby gradually reducing the load on the occupant""s chest.
A similar principle has been used for load limiters that operate in two steps. Such a two-stage system is intended to give a high and relatively even load on the occupant""s chest during the whole crash.
Air bag constructions have also been known, such as described in U.S. Pat. No. 6,036,226, wherein the inflation rate of the air bag is capable of modulation.
As is known, the detrimental effects of a vehicle crashing into another object occurs over a very limited amount of time, typically measured in milliseconds. Accordingly, restraint systems, such as seat belts and air bags, have a very limited time within which to react and deploy.
Further, in many cases, the design and construction of seat belts and air bags have been based upon standards developed from the results obtained in experimental crashes performed with dummies placed in a vehicle. Typically, these standards have been based upon an xe2x80x9caveragexe2x80x9d occupant seated in a particular position. Accordingly, in actual vehicle crashes, occupants having quite different characteristics from the xe2x80x9caveragexe2x80x9d occupant and seated in different manners from the standard seating position, may have forces imposed thereon by the seat belts and air bags that actually harm the occupant.
Accordingly, it is an object of the invention to program a seat belt assembly to react to the forces that are generated during a vehicle crash.
It is another object of the invention to be able to program a seat belt assembly during a crash in a manner to reduce the risk of injury to an occupant.
It is another object of the invention to be able to program a seat belt assembly to respond to the characteristics of a seated occupant during a crash.
Briefly, the invention is directed to a seat belt assembly for an occupant of a vehicle that is typically used with an air bag.
The seat belt assembly includes an electronically controlled seat belt module that is mounted in the vehicle, a buckle receiving unit of conventional type for anchoring one end of a seat belt about an occupant seated in the vehicle and a central processing unit (CPU) that is operatively connected to the module to operate the module.
The electronically controlled seat belt module includes a shaft, a spool that is rotatably mounted concentrically of the shaft for winding of a seat belt thereon, a plurality of poles mounted on the shaft and a plurality of poles mounted on the spool in alternating relation with the poles on the shaft. In addition, a magneto-rheological fluid (M-R fluid) is disposed between the poles of the shaft and the spool and an electromagnetic coil is mounted between the shaft and spool to create a magnetic field passing through the poles and fluid upon actuation of the electromagnetic coil.
The central processing unit is operatively connected to the electromagnetic coil of the module for delivering a programmed electric current over time to the electromagnetic coil. For example, at the onset of a crash, the CPU delivers an electric current over time to the coil to create a magnetic field that is sufficient to have the M-R fluid initially lock the spool against rotation relative to the shaft. Subsequently, the CPU delivers a reduced electric current over time to the coil to release the spool at a specific rate and profile in order to minimize the belt load on the occupant during a crash.
The seat belt assembly may be constructed so that in the event a pre-crash event is detected by a sensor in the vehicle or an actual crash is sensed by a sensor in the vehicle, a signal is delivered to the CPU that, in turn, is programmed to respond by first delivering a signal to the module to tension the seat belt to eliminate slack in the belt. For example, the CPU delivers a signal to an electric rewind motor in the module to rewind the spool. In this respect, the central processing unit delivers a specific current for tension or load limitation profile to the motor. The tension force and load limitation force may be variable and can depend on occupant classification, driving speed and crash sensor. These data are processed by the central processing unit and used to control the seat belt module.
After tensioning of a seat belt has reached a maximum force, the seat belt spool is electronically locked via a second signal forwarded by the CPU to the coil in the module.
As the kinetic energy of the occupant in an emergency situation begins to generate a load on the locked seat belt, belt forces on the chest and abdomen of the occupant increase rapidly and are sensed by a seat belt tension sensor of conventional construction. When the belt forces reach a maximum allowed limit, a signal is emitted to the CPU which, in turn, delivers a responsive signal to the coil in the module in order to reduce the strength of the magnetic field on the M-R fluid. As a result, the seat belt spool is released from a locked condition and allowed to rotate at a specific rate and profile to unwind the seat belt and thereby gradually reduce the belt load on the chest and abdomen of the occupant.
Typically, the response time for the CPU to lock the spool or to release the spool at the required profile is 5 to 10 milliseconds. This allows the electronically controlled seat belt module to deliver a safer and gradual absorbing energy to the occupant and a controlled interface with an air bag that is being deployed to cushion the occupant.
In accordance with the invention, the maximum belt force limits are variable and determined by the CPU and are dependent on occupant classification, crash severity, occupant position and air bag deployment profile.
The module can also operate in a simplier mode utilizing preprogrammed information collected during vehicle crash research. In that mode, the module would utilize information from a reduced number of sensors. For instance, information from an occupant weight sensor and/or crash severity sensor may be sufficient to select the appropriate current profile. Other combinations of sensors providing information to the module are also possible.
The module may be constructed with a spool that is mounted on a fixed shaft and that can be driven by a motor. Alternatively, the module may be constructed with a spool mounted on a rotatable shaft which, in turn, is driven by a motor.
In still other embodiments, the module may be constructed to cooperate with a pretensioner in which case a motor may not be required. In these embodiments, the shaft may be fixed or rotatable.
In still other embodiments, the module may be constructed with the poles disposed concentrically of the shaft and spool or disposed perpendicularly of the shaft and spool.